Method of fabricating a light emitting diode chip having phosphor coating layer

ABSTRACT

A method of fabricating light emitting diode chips having a phosphor coating layer comprises providing a substrate having a plurality of light emitting diodes formed thereon; forming a conductive bump on at least one of the plurality of light emitting diodes; forming a phosphor coating layer over the substrate and the light emitting diodes; cutting the phosphor coating layer by a point cutter to remove an upper portion of the phosphor coating layer, so as to reduce a thickness of the phosphor coating layer and expose the conductive bump; and forming a plurality of individual light emitting diode chips having the phosphor coating layer by separating the plurality of light emitting diodes.

RELATED APPLICATIONS

This application is based upon and claims the benefit of priority toTaiwan Patent Application No. 099108042, filed Mar. 18, 2010, the entirecontent of which is incorporated by reference herein in its entirety.

TECHNOLOGY FIELD

The present invention relates to a method of fabricating a lightemitting diode chip, and particularly to a method of fabricating a lightemitting diode chip having a uniform phosphor coating layer.

BACKGROUND

Due to their long lifetime, small size, high resistance to shock andvibration, low heat generation, and low power consumption, lightemitting diodes (LEDs) have been widely used in display or as lightsource in various consumer electronic devices, electrical appliances,and apparatuses. Recently, multi-color and high brightness LEDs havealso been used in out-door large-screen displays, traffic lights, etc.In the future, LEDs may act as the major illumination light source, withthe advantages of energy saving as well as environment protection.

One common type of LED is the white LED, which is capable of emittingwhite light. Different approaches can be implemented to realize whitelight emitting from an LED. One approach is to use the combination of ablue LED chip and yellow phosphor. FIG. 1 shows the cross-sectional viewof a prior art white LED. The conventional white LED 100 shown in FIG. 1comprises a blue LED chip 110 arranged on a base 120. The blue LED chip110 is electrically connected to the base 120 by electrical wires W. Ayellow phosphor resin 130 is formed to cover the blue LED chip 110 andthe wires W by dispensing, for example. A lens 140 is formed over theyellow phosphor resin 130. The blue light emitted by the blue LED chip110 is partially absorbed by the yellow phosphor powders in the yellowphosphor resin 130 and converted to yellow light. Unabsorbed blue lightmixes with the yellow light so as to generate a white light.

However, there are problems with such convention LEDs in that it isoften difficult for the yellow phosphor resin 130 formed by dispensingto evenly cover the LED chip. A thicker portion of the yellow phosphorresin 130 absorbs more blue light and emits more yellow light than athinner portion. Accordingly, it is difficult for such an LED 100 toemit light with uniform color. For example, while it may be possible torealize white light in the center portion of the yellow phosphor resin130, light emitted from other portion of the yellow phosphor resin 130may undesirably appear yellowish.

SUMMARY

In the following description, certain aspects and embodiments willbecome evident. It should be understood that the aspects andembodiments, in their broadest sense, could be practiced without havingone or more features of these aspects or embodiments. Thus, it should beunderstood that these aspects and embodiments are merely exemplary andnot restrictive.

In accordance with one aspect of the disclosure describing embodimentsof the present invention, there is provided a method of fabricatinglight emitting diode chips having a phosphor coating layer. In thefabrication method, a substrate is provided having a plurality of lightemitting diodes formed thereon. A conductive bump is formed on at leastone of the plurality of light emitting diodes. A phosphor coating layeris formed over the substrate and the light emitting diodes and is cut bya point cutter to remove an upper portion of the phosphor coating layer,so as to reduce a thickness of the phosphor coating layer and expose theconductive bump. A plurality of individual light emitting diode chipshaving the phosphor coating layer are formed by separating the pluralityof light emitting diodes.

Features and advantages consistent with the invention will be set forthin part in the description which follows, and in part will be obviousfrom the description, or may be learned by practice of the invention.Such features and advantages will be realized and attained by means ofthe elements and combinations particularly pointed out in the appendedclaims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a prior art white lightemitting diode.

FIGS. 2A-2E are cross-sectional views showing an exemplary process offabricating light emitting diode chips according to one embodiment ofthe invention.

FIGS. 3A-3B are a plan view and a side view, respectively, illustratingthe rotating direction of the diamond cutter and the moving direction ofthe semiconductor wafer during the cutting step shown in FIG. 2C.

FIGS. 4A-4E are cross-sectional views showing an exemplary process offabricating light emitting diode chips according to another embodimentof the invention.

FIG. 5 is a enlarged view illustrating an exemplary light emitting diodechip shown in FIG. 4A.

DETAILED DESCRIPTION

Embodiments consistent with the invention include methods of fabricatingone or more light emitting diode chips having a uniform phosphor coatinglayer. Hereinafter, embodiments consistent with the present inventionwill be described with reference to the drawings. Wherever possible, thesame reference numbers will be used throughout the drawings to refer tothe same or like parts.

FIGS. 2A-2E show an exemplary process of fabricating one or more lightemitting diode chips according to one embodiment of the invention.Referring now to FIG. 2A, an exemplary substrate C is first provided. Alight emitting unit 210 is formed over the substrate C. The lightemitting unit 210 may comprise a first semiconductor layer 212 with afirst conductivity type, a light emitting layer 214, and a secondsemiconductor layer 216 with a second conductivity type. The lightemitting layer 214 may be sandwiched between the first semiconductorlayer 212 and the second semiconductor layer 216. The substrate C may bemade of, for example, silicon carbide (SiC), silicon (Si), sapphire,zinc oxide (ZnO), gallium arsenide (GaAs), spinel (MgAl₂O₄), or metal(such as copper). A plurality of electrodes 220 are formed on the secondsemiconductor layer 216 and a plurality of conductive bumps 230 are thenformed on the electrodes 220. The conductive bumps may be made of, forexample, gold (Au) or gold alloy.

Referring now to FIG. 2B, a phosphor coating layer 240 is formed overthe second semiconductor layer 216 and the conductive bumps 230. Thephosphor coating layer 240 may cover the conductive bumps 230. In someembodiments, the phosphor coating layer 240 may be formed by, forexample, transfer molding, compressing molding, screen printing, spincoating, dispensing, electrophoresis, spray coating, or any othersuitable methods. In one embodiment, the phosphor coating layer 240 maybe a mixture of at least one type of phosphor powder and a resin. Theresin may be, for example, silicone or epoxy resin.

After forming the phosphor coating layer 240 over the secondsemiconductor layer 216 and the conductive bumps 230, the phosphorcoating layer 240 may be subjected to curing. Then, as shown in FIG. 2C,an upper portion of the cured phosphor coating layer 240′ is removed bycutting the phosphor coating layer 240′ using a point cutter, e.g., adiamond cutter or a Tungsten Carbide(WC) cutter (not shown), to reducethe thickness of the cured phosphor coating layer 240′ so that theconductive bumps 230 are exposed. The conductive bumps 230 are exposedso as to facilitate the subsequent wire bonding process. It is to benoted that the step of cutting the phosphor coating layer 240′ may beperformed multiple times. After each cutting step, the wafer may bechecked to see whether the conductive bumps 230 are exposed. If theconductive bumps 230 are not exposed, the cutting step is repeated. Suchprocedure may be repeatedly performed until the conductive bumps 230 areexposed.

Referring now to FIGS. 3A and 3B, a plan view and a side view,respectively, of the phosphor coating layer 240′ of FIG. 2C are shown toillustrate how the diamond cutter moves relative to the semiconductorwafer during cutting of the phosphor coating layer 240′. In oneembodiment, when cutting the phosphor coating layer 240′, the diamondcutter 250 may rotate clockwise about a rotation axis in the verticaldirection. The wafer may move relative to the diamond cutter 250 in thehorizontal direction indicated by V. However, the rotation direction ofthe diamond cutter 250 and the moving direction of the wafer are notlimited to those described above. For example, the diamond cutter 250may also rotate counter-clockwise. In some embodiments, the diamondcutter 250 may also cut the conductive bumps 230, and in the meantime,an upper portion of the conductive bumps 230 is removed.

It is to be noted that, in a conventional chemical mechanical polishingmethod, polishing slurry comprising abrading particles and a polishingpad having abrading particles are needed. During polishing, thepolishing slurry and the material polished from the polishing surfacecannot be removed instantaneously. Therefore, when a chemical mechanicalpolishing method is used to polish the phosphor coating layer, it isdifficult to keep the upper surface of the phosphor coating layer at thesame level as the upper surface of the conductive bumps due to thedifferent degree of hardness between the phosphor coating layer and theconductive bumps. On the other hand, consistent with an embodiment andprinciples of the present invention, the diamond cutter 250 may cut thephosphor coating layer 240′ and the conductive bumps 230 at the sametime, and may push away the material cut from the phosphor coating layer240′ and/or that cut from the conductive bumps 230 immediately. In sucha manner, the upper surface of the phosphor coating layer 240′ and thatof the conductive bumps 230 may be kept at the same height level afterthe cutting step, as shown in FIGS. 2C-2E and 3B.

Consistent with an embodiment and principles of the present invention,the diamond cutter 250 cuts the phosphor in the horizontal direction.Therefore, the phosphor layer 240′ after cutting has a substantiallyuniform thickness, which may be about 5 μm to about 40 μm. For example,the thickness of the phosphor layer 240′ after cutting may be about 30μm.

Due to the rotation of the diamond cutter 250, the tip of the diamondcutter moves in a circle when cutting the phosphor coating layer 240′,and then forming a curved cutting line on the surface of the wafer asshown in FIG. 3. In addition, since the wafer moves relative to thediamond cutter 250 in the direction V, the cutting line is then expandedto a cutting surface, so that the entire phosphor coating layer 240′ issubjected to cutting and an upper portion of the entire phosphor coatinglayer 240′ may be removed by the cutting step. The surface 244 of thephosphor coating layer 240′ after cutting may have regular patterns.These patterns may help to reduce the total reflection of the lightemitted from the light emitting layer 214 and/or that emitted by thephosphor coating layer 240 at the surface 244 of the phosphor coatinglayer 240′, and thus may improve the extraction efficiency.

Referring now to FIG. 2D, a plurality of individual light emitting diodechips 200 having a phosphor coating layer 240′ may be formed by cuttingor otherwise separating the phosphor coating layer 240′, the lightemitting unit 210, and the substrate C along the vertical dashed linesin the spaces G between the conductive bumps 230. Such separating may beaccomplished via, for example, dicing with a blade or laser cutting.FIG. 2E is an enlarged view showing such a light emitting diode chip 200after the separating step. The light emitting diode chip 200 shown inFIG. 2E comprises two conductive bumps. However, it is noted that thenumber of conductive bumps comprised in one light emitting diode chipmay not be limited to two. A light emitting diode chip consistent withan embodiment and principles of the present invention may comprise,e.g., one, three, or more conductive bumps. A larger light emittingdiode chip may have more conductive bumps, so that uniformity of thecurrent distribution may be improved.

Consistent with principles of the present invention, different equipmentmay be used to dice the phosphor coating layer 240′, the light emittingunit 210, and the substrate C. For example, the phosphor coating layer240′, the light emitting unit 210, and the substrate C may be dicedusing a blade. Alternatively, the phosphor coating layer 240′ and thelight emitting unit 210 may be diced using a blade, and the substrate Cmay be diced using a laser. As another alternative, the phosphor coatinglayer 240′, the light emitting unit 210, and the substrate C may bediced using a laser.

Consistent with principles of the present invention, since the phosphorcoating layer 240′ is first formed over the light emitting unit 210 andthen cutting is performed on the phosphor coating layer 240′ to reduceits thickness, the phosphor coating layer may be controlled to form onlyon the upper surface of the light emitting unit 210. Moreover, thethickness of the phosphor coating layer formed on the upper surface ofthe light emitting unit may have a substantially uniform thickness.Therefore, the light emitted by the light emitting diode chip in anembodiment of the invention may have better uniformity. That is, uniformwhite color may be emitted from the entire upper surface of the phosphorcoating layer of the light emitting diode chip.

FIGS. 4A-4E show an exemplary process of fabricating light emittingdiode chips according to another embodiment of the invention. FIG. 5 isan enlarged view of a light emitting diode shown in FIG. 4A.

Referring to FIGS. 4A and 5, a submount 410 is provided with a pluralityof light emitting diodes 420 formed thereon. Each light emitting diode420 may comprise a substrate 422, a first semiconductor layer 424 with afirst conductivity type, a light emitting layer 426, and a secondsemiconductor layer 428 with a second conductivity type. The lightemitting layer 426 may be sandwiched between the first semiconductorlayer 424 and the second semiconductor layer 428. The submount 410 maybe print circuit board, ceramic submount, silicon submount, or metalsubmount. The substrate 422 may be made of, for example, sapphire.

As shown in FIG. 4A, a recess R may be formed in the light emittingdiode 420, exposing portion of the first semiconductor layer 424. Afirst electrode P1 is formed over the portion of the first semiconductorlayer 424 exposed in the recess R. A second electrode P2 is formed overthe second semiconductor layer 424.

Next, referring to FIG. 4B, a first conductive bump 432 and a secondconductive 434 are formed over the first electrode P1 and the secondelectrode P2, respectively. The top point of the first conductive bump432 and that of the of the second conductive bump 434 may be kept atapproximately the same height level.

Referring to FIG. 4C, a phosphor coating layer 440 is then formed overthe submount 410, the light emitting diode chips 420, the firstconductive bumps 432 and the second conductive bumps 434. The phosphorcoating layer 440 may fill the spaces G1 between the light emittingdiode chips. In some embodiments, the phosphor coating layer 440 may beformed by, for example, transfer molding, compressing molding, screenprinting, spin coating, dispensing, electrophoresis, spray coating, orany other suitable methods. The phosphor coating layer 440 may be amixture of at least one type of phosphor powder and a resin. The resinmay be, for example, silicone or epoxy resin.

After forming, the phosphor coating layer 440 is subjected to curing.Then, as shown in FIGS. 4C and 4D, an upper portion of the curedphosphor coating layer 440′ is removed by cutting the phosphor coatinglayer 440′ using a point cutter, e.g., a diamond cutter 450, to reducethe thickness of the phosphor layer 440′ so that the first conductivebumps 432 and the second conductive bumps 434 are exposed. In someembodiments, when cutting the phosphor coating layer 440′, the diamondcutter 450 may also cut the first upper end portions 432 a of the firstconductive bumps 432 and the second upper end portions 434 a of thesecond conductive bumps 434.

Consistent with the present invention, since the diamond cutter 450 maycut the phosphor coating layer 440′, the first upper end portions 432 aof the first conductive bumps 432, and the second upper end portions 434a of the second conductive bumps 434 at the same time, the upper surface444 of the phosphor coating layer 440′, the first upper surfaces 432 bof the first conductive bumps 432, and the second upper surfaces 434 bof the second conductive bumps 434 may be kept at substantially the sameheight level after the cutting step, as shown in FIG. 4D.

Consistent with principles of the present invention, since the diamondcutter 450 cuts the phosphor coating layer 440 in a rotation manner(same to that shown in FIGS. 2C, 3A, and 3B), the surface 444 of thephosphor coating layer 440′ after cutting may have regular patterns.These patterns may help to reduce the total reflection of the lightemitted from the light emitting diode chips 420 and/or that emitted bythe phosphor coating layer 440′ at the surface 444 of the phosphorcoating layer 440′, and thus may improve the extraction efficiency.

Then, referring to FIG. 4D, the phosphor coating layer 440′ and thesubmount 410 are diced along the vertical dashed lines in the spaces G1between the light emitting diode chips 420, so as to form a plurality ofindividual light emitting diode chips 400 having a phosphor coatinglayer. One of the light emitting diode chips 400 is shown in FIG. 4E.Consistent with principles of the present invention, different equipmentmay be used to dice the phosphor coating layer 440′ and the submount410. For example, the phosphor coating layer 440′ and the submount 410may be diced using a blade. Alternatively, the phosphor coating layer440′ may be diced using a blade, and the submount 410 may be diced usinga laser. As another alternative, the phosphor coating layer 440′ and thesubmount 410 may be diced using a laser.

In one embodiment, since the phosphor coating layer 440′ is first formedover the light emitting diode chips 420 and then cutting is performed onthe phosphor coating layer 440′ to reduce its thickness, the phosphorcoating layer thus formed on the light emitting diode chips may have asubstantially uniform thickness. Therefore, the light emitted by thelight emitting diode chip consistent with the present invention may havebetter uniformity.

In one embodiment, since the light emitting diode chips 420 are providedover the submount 410, the phosphor coating layer 440′ may fully fillthe space between the chips. Therefore, the phosphor coating layer mayalso be formed on the side surface S of the light emitting diode chip420. The thickness of the phosphor coating layer formed on the sidesurface S may be controlled to be smaller than the thickness of thephosphor coating layer formed on the upper surface of the light emittingchip. Since the light emitted from the side surface S of the lightemitting diode chip 420 is relatively weaker, thinner phosphor coatinglayer on the side surface may help to ensure better uniformity andhigher brightness across the entire light emitting diode chip includingthe upper surface and the side surface.

In summary, an embodiment of the present invention may use a diamondcutter to cut the phosphor coating layer so as to reduce the thicknessof the phosphor coating layer. The formed phosphor coating layer aftercutting has very uniform thickness. Therefore, the light emitted fromthe light emitting diode chip having phosphor coating layer consistentwith the present invention may have good uniformity. In anotherembodiment, since the ratio between the vertical thickness and thelateral thickness of the phosphor coating layer on the upper surface andthe side surface, respectively, of the light emitting diode chip may becontrolled, good light uniformity may be achieved across the entirelight emitting diode chip. Moreover, since the surface of the phosphorcoating layer after cutting may have regular patterns, the totalreflection at the surface of the phosphor coating layer may be reduced,so that the extraction efficiency of the light emitting diode chip maybe improved.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A method of fabricating a plurality of light emitting diode chipshaving a phosphor coating layer, comprising: providing a substratehaving a plurality of light emitting diodes formed thereon; forming aconductive bump on at least one of the plurality of light emittingdiodes; forming the phosphor coating layer over the substrate and thelight emitting diodes; cutting the phosphor coating layer with a pointcutter to remove an upper portion of the phosphor coating layer, so asto reduce a thickness of the phosphor coating layer and expose theconductive bump, the cutting comprising: rotating the point cutter abouta rotation axis in a vertical direction; and moving the substraterelative to the point cutter in a horizontal direction; and forming aplurality of individual light emitting diode chips having the phosphorcoating layer by separating the plurality of light emitting diodes. 2.The method of claim 1, wherein the point cutter is a diamond cutter or aTungsten Carbide(WC) cutter.
 3. The method of claim 1, wherein the pointcutter cuts the upper portion of the phosphor coating layer in ahorizontal direction.
 4. The method of claim 1, further comprisingcutting an upper portion of the conductive bump by the point cutter. 5.The method of claim 4, wherein, after cutting, an upper surface of thephosphor coating layer is substantially at the same level as an uppersurface of the conductive bump.
 6. The method of claim 1, whereincutting the phosphor coating layer comprises: cutting the phosphorcoating layer to remove a surface layer of the phosphor coating layer;checking whether the conductive bump is exposed; and if the conductivebump is not exposed, repeating the cutting step until the conductivebump is exposed.
 7. The method of claim 1, wherein the phosphor coatinglayer is formed by one of transfer molding, compressing molding, screenprinting, spin coating, dispensing, electrophoresis and spray coating.8. The method of claim 1, wherein forming the plurality of individuallight emitting diode chips having the phosphor coating layer comprisesdicing the phosphor coating layer, the light emitting diodes, and thesubstrate.
 9. The method of claim 8, wherein the step of dicing isperformed by a blade or a laser.
 10. The method of claim 8, wherein thestep of dicing further comprises: dicing the phosphor coating layer andthe light emitting diodes with a blade, and dicing the substrate with alaser.
 11. The method of claim 1, wherein: the plurality of lightemitting diodes comprises a plurality of light emitting diode diesformed separately on the substrate, and wherein the step of forming thephosphor coating layer further comprises filling a space between thedies.
 12. The method of claim 11, wherein forming the plurality ofindividual light emitting diode chips having the phosphor coating layercomprises dicing the phosphor coating layer and the substrate.
 13. Themethod of claim 12, wherein the step of dicing is performed by a bladeor laser.
 14. The method of claim 13, wherein the step of dicing furthercomprises: dicing the phosphor coating layer and the light emittingdiodes with a blade, and dicing the substrate with a laser.
 15. Themethod of claim 11, wherein the substrate is a printed circuit board, aceramic substrate, a silicon substrate, or a metal substrate.
 16. Themethod of claim 1, wherein the step of cutting results in an uppersurface of the phosphor coating layer having a rough surface withregular patterns.
 17. The method of claim 1, wherein the step of cuttingresults in the phosphor coating layer having a substantially uniformthickness.
 18. The method of claim 1, wherein the step of forming thephosphor coating layer further comprises mixing at least a phosphorpowder and a resin, the resin being a silicone or an epoxy.
 19. Themethod of claim 1, wherein the step of forming the conductive bumpfurther comprises forming the conductive bump from Au or alloy of Au.20. The method of claim 1, wherein the substrate is a SiC substrate, aSi substrate, a sapphire substrate, a ZnO substrate, a GaAs substrate, aspinel substrate, or a metal substrate.